Obtaining Trees.

Please note that Trees obtained this way will contain Stub
items. These need to be executed (they are IO actions) in order to be
accessed. Use expand to do this. However, many operations are
perfectly fine to be used on a stubbed Tree (and it is often more
efficient to do everything that can be done before expanding a Tree).

Take a relative FilePath and turn it into an AnchoredPath. The operation
is (relatively) unsafe. Basically, by using floatPath, you are testifying
that the argument is a path relative to some common root -- i.e. the root of
the associated Tree object. Also, there are certain invariants about
AnchoredPath that this function tries hard to preserve, but probably cannot
guarantee (i.e. this is a best-effort thing). You should sanitize any
FilePaths before you declare them good by converting into AnchoredPath
(using this function).